Nanostructured films of amphiphilic fluorinated block copolymers for fouling release application.
New amphiphilic block copolymers S nSz m consisting of blocks with varied degrees of polymerization, n and m, of polystyrene, S, and polystyrene carrying an amphiphilic polyoxyethylene-polytetrafluoroethylene chain side-group, Sz, were prepared by controlled atom transfer radical polymerization (ATRP). The block copolymers, either alone or in a blend with commercial SEBS (10 wt% SEBS), were spin-coated in thinner films (200-400 nm) on glass and spray-coated in thicker films ( approximately 500 nm) on a SEBS underlayer (150-200 microm). Angle-resolved X-ray photoelectron spectroscopy (XPS) measurements proved that at any photoemission angle, varphi, the atomic ratio F/C was larger than that expected from the known stoichiometry. Consistent with the enrichment of the outer film surface (3-10 nm) in F content, the measured contact angles, theta, with water (theta w > or = 107 degrees ) and n-hexadecane (theta h > or = 64 degrees ) pointed to the simultaneous hydrophobic and lipophobic character of the films. The film surface tension gamma S calculated from the theta values was in the range 13-15 mN/m. However, the XPS measurements on the "wet" films after immersion in water demonstrated that the film surface underwent reconstruction owing to its amphiphilic nature, thereby giving rise to a more chemically heterogeneous structure. The atomic force microscopy (AFM) images (tapping mode/AC mode) revealed well-defined morphological features of the nanostructured films. Depending on the chemical composition of the block copolymers, spherical (ca. 20 nm diameter) and lying cylindrical (24-29 nm periodicity) nanodomains of the S discrete phase were segregated from the Sz continuous matrix (root-mean-square, rms, roughness approximately 1 nm). After immersion in water, the underwater AFM patterns evidenced a transformation to a mixed surface structure, in which the nanoscale heterogeneity and topography (rms = 1-6 nm) were increased. The coatings were subjected to laboratory bioassays to explore their intrinsic ability to resist the settlement and reduce the adhesion strength of two marine algae, viz., the macroalga (seaweed) Ulva linza and the unicellular diatom Navicula perminuta. The amphiphilic nature of the copolymer coatings resulted in distinctly different performances against these two organisms. Ulva adhered less strongly to the coatings richer in the amphiphilic polystyrene component, percentage removal being maximal at intermediate weight contents. In contrast, Navicula cells adhered less strongly to coatings with a lower weight percentage of the amphiphilic side chains. The results are discussed in terms of the changes in surface structure caused by immersion and the effects such changes may have on the adhesion of the test organisms.
Martinelli
Elisa
E
Dipartimento di Chimica e Chimica Industriale and UdR Pisa INSTM, Universita di Pisa, via Risorgimento 35, 56126 Pisa, Italy.
Agostini
Serena
S
Galli
Giancarlo
G
Chiellini
Emo
E
Glisenti
Antonella
A
Pettitt
Michala E
ME
Callow
Maureen E
ME
Callow
James A
JA
Graf
Katja
K
Bartels
Frank W
FW
D000818:Animals; D001966:Bromine / Q000737:chemistry; D017377:Diatoms; D056890:Eukaryota / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D018625:Microscopy, Atomic Force; D049329:Nanostructures / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry; D011108:Polymers / Q000737:chemistry*; D011137:Polystyrenes / Q000737:chemistry; D011138:Polytetrafluoroethylene / Q000737:chemistry; D012624:Seaweed; D012828:Silicones / Q000737:chemistry; D013052:Spectrometry, X-Ray Emission / Q000379:methods; D013499:Surface Properties
D011108:Polymers; D011137:Polystyrenes; D012828:Silicones; D011092:Polyethylene Glycols; D011138:Polytetrafluoroethylene; D001966:Bromine